Characteristics of fuse resistance and its difference from ordinary resistance
time:2021-10-11Under normal conditions, the safety resistor has the function of ordinary resistance. Once the circuit fails and exceeds its rated power, it will disconnect the circuit within the specified time, so as to protect other components. The safety resistor is divided into two types: irreparable type and repairable type. Next, guanfa technology will talk about the characteristics of safety resistance and the difference between safety resistance and ordinary resistance.
function
It plays the dual role of fuse and resistance in the circuit diagram. It is mainly used in the output circuit of power supply circuit and the output circuit of secondary power supply. They generally have low resistance (several ohms to tens of ohms) and low power (1 / 8 ~ 1W). Their function is to fuse in time in case of overcurrent to protect other components in the circuit from damage.
In case of short-circuit fault and overcurrent of circuit load, the temperature of safety resistor will rise to 500 ~ 600 ℃ in a very short time. At this time, the resistance layer will be peeled off and fused, which plays the role of safety and improves the safety of the whole machine.
Discrimination method
Although fuse resistors are widely used in power supply circuits, the marking methods in circuit diagrams of countries and manufacturers are different. Although the marking symbols are not unified at present, they have common characteristics:
(1) They are obviously different from the marking of general resistance, which is easy to judge in the circuit diagram.
(2) It is generally used in low-voltage or high-voltage circuits with large current capacity of power circuit or secondary power supply.
(3) There is only one color ring on the fuse resistor. As shown in the attached figure, the color of the color ring represents the resistance value.
(4) In the circuit, the safety resistor is a long leg welded on the circuit board (generally, the resistor is welded close to the circuit board), which is far away from the circuit board, which is convenient for heat dissipation and differentiation.
Specification standard
(1) RN1 / 4W, 10 Ω safety resistor, color ring is black, power is 1 / 4W; When 8.5V DC voltage is applied to both ends of the safety resistor, the resistance increases to more than 50 times of the initial value within 60 seconds.
(2) RN1 / 4W, 2.2 Ω safety resistor, red color ring, power 1 / 4W; When 3.5A current passes through, the resistance increases to more than 50 times the initial value within 2 seconds.
(3) RN1 / 4W, 1 Ω safety resistor, color ring is white, power is 1 / 4W; When 2.8A AC current passes through, the resistance increases to more than 400 times the initial value within 10 seconds.
How to distinguish between ordinary resistance and safety resistance
Both have the function of resistance, but the resistance fuse is equal to the resistance plus fuse. When the added power exceeds the power of the resistance, the fuse will burn out and the whole resistance will not smoke. The resistance will burn and smoke when the added power exceeds its own power.
